Styrene, an important commodity chemical used to make plastics, is generally made by the dehyrogenation of ethylbenzene. The intermediate ethylbenzene may be derived as a by-product of catalytic reforming or by alkylating benzene with ethylene.
Cumene or isopropylbenzene is also a commodity chemical used for making phenol and .alpha.-methylstyrene. It may be derived from distillation of coal tar or petroleum or by the alkylation of benzene with propylene.
U.S. Pat. No. 4,107,224; which is hereby incorporated by reference, discloses a process for ethylating benzene by contacting benzene and a dilute ethylene stream with a ZSM-5 type zeolite. The molar concentration of ethylene in the dilute ethylene stream is generally more than 15 percent. The molar concentration of carbon monoxide is generally less than 5 percent. The hydrogen to carbon monoxide ratio is also high.
The Fischer-Tropsch process as practiced commercially today is described in Chapter 4 of Catalysis, Science and Technology, Vol. 1, by M. E. Dry which is incorporated herein by reference. In general, a carbonaceous material is first gasified to hydrogen and carbon monoxide. This raw gas is then purified and passed through a catalytic Fischer-Tropsch reactor. Water, carbon dioxide and hydrocarbons and oxygenates which are liquid at ambient temperatures are separated from the gases. The gaseous products including unconverted hydrogen and carbon monoxide and the hydrocarbons having 4 or less carbons, are then cryogenically separated into the various components. Purified ethylene may then be reacted with aromatic hydrocarbons in the presence of heterogeneous alkylation catalysts such as described in U.S. Pat. No. 3,751,506; which is herein incorporated by reference.
Due to the low boiling points of hydrogen and carbon monoxide, the Fischer-Tropsch process is generally run at a conversion of at least 60 percent and preferably at least 80 percent to reduce the amount of hydrogen and carbon monoxide that must be separated from the light hydrocarbons. A disadvantage of operating the Fischer-Tropsch process at high conversions is that the selectivity to ethylene is lower.